The identification of Mycobacterium tuberculosis is a critical task for clinical laboratories. Because pulmonary tuberculosis poses a significant threat to both patients and healthcare workers, the collection and handling of specimens must prioritize safety, quality, and speed. The success of any diagnostic test—whether it is a smear, culture, or molecular assay—depends entirely on the quality of the specimen provided.
This guide outlines the standardized protocols for collecting various clinical samples, ensuring maximum pathogen recovery while minimizing risks of aerosolization and contamination.
General Safety and Quality Principles
Pathogen identification relies on two main pillars: Specimen Quality and Appropriate Processing. To maintain a safe environment, clinicians must adhere to the following:
Containment: Open all suspected tuberculosis specimens only within a Class II Biosafety Cabinet (BSC) to prevent the inhalation of infectious aerosols.
Labeling: Clearly label every container as “HIGH RISK” to alert laboratory personnel.
Leak Prevention: Use wide-mouth, sterile, leak-proof containers. Place the primary container into a secondary biohazard bag before transport.
Pulmonary Secretions
Pulmonary secretions remain the most common samples received for TB diagnosis. While sputum is the primary choice, several techniques exist for patients who cannot produce it spontaneously.
1. Sputum Collection
Sputum is the most important specimen for diagnosing pulmonary TB. For the best results, use spontaneously expectorated sputum.
Patient Instruction: Instruct the patient to take a deep breath, hold it for a few seconds, and then perform a deep, vigorous cough.
Precautions: Patients must cover their mouths during coughing to prevent the spread of aerosols. They should not use oral antiseptics (like mouthwash) before collection, as these can inhibit the growth of Mycobacteria.
Rejection Criteria: Laboratories will reject samples consisting only of saliva or nasal secretions, or those containing food particles and other foreign matter.
2. Aerosol Induction Technique
When a patient cannot produce sputum spontaneously, clinicians use saline aerosol induction.
Mechanism: The patient inhales a fine mist of sterile saline. This irritates the airways, inducing a deep cough and facilitating the collection of secretions from the lower respiratory tract.
3. Gastric Lavage
Gastric lavage is a specialized procedure for patients who may have swallowed their sputum during the night.
Target Patients: This is generally limited to children younger than 3 years old, non-ambulatory patients, or senile patients.
The Procedure: A Levine collection tube is inserted through the nose into the stomach. A syringe is attached, and filtered distilled water is introduced. The clinician then withdraws 20–25 ml of gastric contents.
Frequency: Collect a series of specimens over three consecutive days to increase the diagnostic yield.
Non-Pulmonary Specimens
Mycobacterium can infect almost any organ system, requiring a variety of collection methods for extra-pulmonary tuberculosis.
1. Urine Samples
Urine is often used to diagnose renal tuberculosis.
Timing: Collect an Early Morning Voided (EMU) sample.
Volume: Send the whole voided sample for examination.
Note: Twenty-four-hour urine collections are undesirable because excessive dilution and higher contamination levels make concentration difficult.
2. Body Fluids (CSF, Peritoneal, Pericardial)
Tubercular meningitis and serous infections are serious complications, especially in immunocompromised patients.
Volumes: Collect at least 10 ml of Cerebrospinal Fluid (CSF) and 10–15 ml of peritoneal or pericardial fluid.
Clotting Prevention: Pleural and ascitic fluids tend to clot; clinicians should collect these in containers containing trisodium citrate to keep the sample liquid for processing.
3. Blood and Feces
Blood: Disseminated mycobacterial infections are common in HIV-infected patients. Collect blood using routine sterile culture techniques. The best recovery occurs in BACTEC vials or via the Isolator centrifugation system.
Feces: Use a clean, dry, wax-free container. Do not add any diluents or preservatives to the sample.
4. Pus and Abscess Material
Clean the skin thoroughly with alcohol before collection to minimize skin flora contamination.
Collect the sample using a sterile syringe or a swab, depending on the volume of pus available.
Transportation and Storage
Time is of the essence when dealing with Mycobacteria. Rapid transport ensures that contaminating bacteria do not overgrow the slow-growing M. tuberculosis.
Prompt Delivery: Deliver specimens to the laboratory immediately after collection.
Refrigeration: If you expect a delay in processing, you may refrigerate sputum, gastric lavage, and urine samples.
Handling: Always treat these specimens as high-risk infectious agents.
Summary Table: Specimen Requirements
| Specimen Type | Preferred Method/Timing | Required Volume/Container |
| Sputum | Spontaneous cough, early morning | Wide-mouth, sterile, leak-proof |
| Gastric Lavage | Early morning (after overnight fast) | 20–25 ml (via Levine tube) |
| Urine | Early morning voided (EMU) | Full voided volume |
| CSF | Sterile lumbar puncture | Minimum 10 ml |
| Blood | Routine culture technique | BACTEC vial or Isolator system |
